Which of the following devices is BEST suited for servers that need to store private keys?

An HSM is a dedicated hardware device engineered specifically to securely generate, store, and manage cryptographic keys in tamper-resistant hardware. It enforces strict access controls and prevents private key material from ever being exposed in plaintext, making it the industry standard for servers requiring private key protection.

A hardened network firewall filters and monitors network traffic between segments but has no built-in capability to securely store or protect cryptographic private keys.

A solid state disk drive is general-purpose storage media with no inherent cryptographic key protection, hardware access controls, or tamper resistance.

A hardened host firewall is a software-based mechanism controlling traffic on a single host and is not designed or capable of securely storing private key material.